ah, it just doesn't seem far fetched, perhaps as a response to Night Elves accepted mages into their ranks, Blood Elves abandoned their disdain for the more nature-oriented elements suppressed in their culture by magisters.

Isn't there a Blood Elf Druid in one of the TBC dungeons? I guess he's not a "true" druid and is using his powers via technomagical experiments, but why couldn't that be used as a reason? In-game the effects are the same as a natural Druid, but lore-wise a Blood Elf Druid isn't gifted with the power of nature, he/she is mutated via magical experiments.

EDIT: Also, I've always thought the root Zael suggested a couple of posts above is perfectly viable and perhaps even more viable with the gradual political thawing under Lor'themar's regency, post-Kael's betrayal, where the Farstriders seem to have more weight to throw in public discourse than the magisters!

This can be their new colours for the tree form model that Blood Elf Druids have.